U.S. Patent Application No. 2004101172 (Lane) discloses a finger imaging system for receiving the finger of a person being fingerprinted by an automated fingerprint reader. The system includes a finger imaging device having a finger receiving portion for receiving the finger to be fingerprinted. Extending outward from the finger receiving surface is a locator bar that engages a crease of the subject finger when it is in about in the desired position. U.S. Patent Application 2004101171 (Lane et al.) discloses a finger imaging system for receiving and holding a finger of a person being fingerprinted by an automated fingerprint reader. The system includes a finger imaging device having a finger receiving portion and a finger positioning portion, together forming a recess of reducing dimension such that a subject finger forcibly inserted into it is held in a stable position. And finally, U.S. Patent Application No. US2004076314 (Cheng) discloses an apparatus that includes a fingerprint sensor and a guiding means. The sensing site of the fingerprint sensor makes a relative and obtuse angle with a guiding plane of the guiding means. Traditionally, in order to record a fingerprint, ink was applied to a finger and then the finger was “rolled” across a paper or other ink receptive surface to print an image of the fingerprint. Fingerprints left by touching a surface and leaving oil residue are captured forensically by a variety of process techniques that “lift” and reveal the fingerprint.
In more recent years, alternative technologies have been developed that can reveal the fine features within a fingerprint and capture the fingerprint directly from the finger. Electronic sensing technology involves holding the finger on a sensing system as the system detects skin or living tissue differences across the finger area or just a relevant portion of the finger area in order to reveal an image of the fingerprint or in order to create an electronic representation of the fingerprint, for example as a digital file. Examples include but are not limited to optical scanners, electroluminescent pressure sensitive systems, integrated circuits with the ability to measure individual pixel sized capacitance, and more.
The production cost for some types of fingerprint scanning systems is driven by the size of the fingerprint area to be sensed. This is especially true for silicon based or integrated circuit (IC) type sensors. Like most IC's, the larger the IC, the more costly it is to produce assuming equal device geometries and layer count. The production cost of the sensor is directly related to the sensing area, and mass production of sensors the size of a thumb is not optimal when only a relevant portion of a fingerprint needs to be scanned in order to build a fingerprint authentication system. If just a portion of the fingerprint is to be used in order to reduce system cost, then it becomes important to place substantially the same relevant portion of the finger that was originally enrolled upon the sensor for every authentication or identification event.
Clearly a smaller sensor would cost less and, assuming the area of the fingerprint sensed is still necessarily large enough to provide an acceptable matching capability or security level, then the optimal solution would be this smaller sensor, leaving out unneeded portions of the total fingerprint area. The finger guide device invention is a device which may be used to reliably reposition a finger upon a small sensor to enable more efficient identification. The device reduces false rejects caused by failure to position the finger close enough to its original enrollment position or positions so that the sensor can read a matching relevant portion of the fingerprint. The finger guide device reduces the incidence of false rejects by naturally, intuitively, and non-forcibly guiding the subject finger to approximately the same and original enrollment position each time the fingerprint identification system is used. When smaller sensors are used, if the finger is enrolled in a manner that scans one relevant area of the finger, or perhaps several overlapping relevant portions of the fingerprint which are then electronically assembled by a computer into a completed “template” representing a larger area of the original subject's fingerprint than any single scan could produce alone, then the system depends upon a subject person or user being able to touch the sensor consistently in the same approximate place so that a relevant portion of the fingerprint is read by the sensor so that matching and therefore authentication or identification may take place. Failure to replace the finger accurately onto the fingerprint sensor or scanner causes false rejects; or, in other words, because the sensor sees a different area of the fingerprint it cannot match with the previously enrolled area or portions of the fingerprint, it rejects a known subject as not matching. This is a false reject. If the system permits additional attempts, and if the second or subsequent try finally aligns the minutiae containing a relevant potion of the fingerprint originally stored during enrollment with the scanner or sensor, the known subject will then be accepted (identified or “authenticated”). The finger guide reduces the average number of attempts to authenticate known subjects by providing a simple, funnel like or inverted pyramid like guide for the finger that physically but non-forcibly encourages the finger into the correct position so that a relevant portion of the finger is in alignment with the sensor or scanner and provides a variety of tactile and other feedback means for the subject user in order to make it easier to “find” the right position again, even after substantial time has passed between enrollment and the next authentication event. If the finger is in the correct position, but the touch pressure is too hard or too light, the scanner or sensor may capture a distorted image and this may also cause a false reject. The finger guide device also assists users in learning and repeating the correct touch pressure using a variety of feedback means including but not limited to tactile feedback, mechanical motion feedback, audio or visual feedback, the field of possible feedback means being known to those skilled in the art of human factors engineering. In contrast with basic flat surface sensors or even poorly designed sensors, the described false reject rate for untrained subjects can range from ten to twenty percent of all subjects. Systems using the finger guide device will experience less than ten percent false rejects and fingerprint authentication systems using the finger guide device may be optimized for even lower rates of false rejects.